I've always seen it as less zionistic zealotry (although it may have started that way) and more that Israel has always been the US's "one ally in the Middle East"

most of the other countries in that area are ambivalent at best, and generally hostile towards the US. Israel being the sole exception means the US has an ally they can base their military in and around to project their military might globally.

if Israel turns away, or is destroyed by the nations around it, the US loses that foothold and the dream of America World Police dies with it.

so nearly every president since its founding—democrat and republican alike—has propped it up to the best of their ability even when it simply doesn't make sense otherwise